Mixing device



United States Patent [72] Inventors Leendert Johannes van der Windt.

Burgerveen. and Johannes Jansen, Zwinindrecht, Netherlands [21] Appl.No. 755,618 [22] Filed Aug. 27, 1968 [45] Patented Dec. 15, 1970 [73]Assignee Brooks Instrument N. V. Veenendaal, Netherlands [32] PriorityApril 5, 1968 3 3 Netherlands [3 1] 6804893- [54] MIXING DEVICE 8Claims, 3 Drawing Figs.

[52] 0.8. CI. 259/4 [51] Int. Cl. B011 15/04 [50] Field ofSearch 259/4,36, 18, 60, 2, 95

[56] References Cited UNITED STATES PATENTS 2,646,346 7/1953 Coplan259/4X 2,992,084 7/1961 Schropp 259/4X 3.212,?57 10/1965 Martin 259/43,387,827 6/1968 Carlyon Primary Examiner- Robert W. JenkinsAttorney-Paul & Paul ABSTRACT: Device for mixing solid or fluidmaterials or the like in a main liquid, said device comprising avertically arranged substantially cylindrical reservoir for receivingthe materials to be mixed, the bottom of the reservoir being providedwith a nozzle, which is connected to a supply for said main liquid andpositioned to spray said main liquid in substantially horizontal, and,in view of the vertical wall of the reservoir, tangential direction, anoverflow tube, the upper end of which being provided with one or moreinlet openings, being arranged in the reservoir together with a helicalshaped baffle plate the fore edge of which, as seen in the direction ofrotation of the liquid flow, is lying higher than the maximum liquidlevel and the back edge below the lowest inlet point of the overflowtube, the supply for said main liquid being formed by a branch of adelivery pipe of a liquid pump, the liquid from below the overflow tubebeing sucked off by a jet pump being mounted, after the branch, in thedelivery pipe, the liquid level in the reservoir being controlled bymeans of a bypass tube with a valve in it operated by a liquid levelcontrol device.

PATENTEU mm 5 I978 SHEET 1 [IF 3 PATENTED am 51910 SHEET 3 BF 3 MIXINGDEVICE The invention relates to a device for mixing solid or fluidmaterials or the like in a main liquid for obtaining a mixture, or asolution, or a suspension, or the like, said device comprising avertically arranged substantially cylindrical reservoir for receivingthe materials to be mixed.

With the known devices of this type generally a stirring device isarranged in the reservoir for mixing the main liquid with the solid orfluid materials. Then the mixture is, by means of a pump, sucked fromthe reservoir for being fed to the location where it is used.

The stirring device and its drive form a considerable part of the costsof the total mixing device. In many cases certain parts of the stirringdevice must, in order to obtain a reliable device, be executed incorrosion resistant materials, while especially with the working up offire-risky materials, the drive of the stirring device, which, in mostinstances, comprises an electromotor, has be to explosionproof.

In practice it further appears that with such devices a sufficient andcorrect mixing is not always obtained, among other things because, evenwith well-dimensioned reservoirs and,

stirring devices, dead corners originate where the velocity of theliquid is too low and the material to be mixed sags. Indeed it'has beentried to prevent this by arranging baffle plates. This increases thecosts, and the stirring device, is less accessible and consequently moredifficult to clean.

A further objection of the use of a stirring device is that air bubbles,or generally gas bubbles, can land in the liquid and are carried awaywith the mixture. This can give difficulties when using the mixture,while the capacityof the suction pump will also'be affected.

The invention now aims at removing the above-mentioned objections andfor this purpose provides a device, which is characterized in that inthe reservoir, near its bottom, and eventually at the locations suitablefor this, at least one nozzle has been arranged connected to a supplyfor said main liquid and positioned to spray said main liquid insubstantially horizontal and, in view of the vertical wall of thereservoir, tangential direction. In the reservoir an overflow tube hasbeen placed the upper end of which is provided with one or more inletopenings, in such a way, that the liquid in the reservoir follows ahelical path with an upwardly directed pitch. At the top of thereservoir, all round a part of the periphery of the overflow tube, ahelical shaped baffle plate running substantially radially to the wallof the reservoir has been mounted. The pitch of this baffle seen in thedirection of rotation of the flow of the liquid, is oppositely directedto the pitch of the flow of the liquid while, seen in the direction ofrotation, the fore edge of the baffle plate lies higher than the maximumliquid level and the baffle plate extends below the minimum liquid leveland somewhat beyond the lowest inlet point of the overflow tube.

By using the nozzle the whole bottom surface of the reservoir iscovered, so that a flow of liquid rotating about the overflow tubeoriginates with an upwardly directed velocity component. Because of thisrotational movement a considerable vortex originates, which vortexcontributes to a close mixing of the materials. When the liquid arrivesat the highest level the helical baffle plate causes a velocitycomponent in the downward direction, owing to which mixing takes placewith the liquid coming from below. This mixing is further improved bythe appearing whirls.

According to a preferred embodiment of the invention the inlet openingin the overflow tube is formed by a vertical slot in said tube wherebyeven with a varying liquid level a correct discharge of the liquid outof the reservoir and into the overflow tube is guaranteed. i

In order to insure that the liquid flowing into the overflow tube, hasas smooth a flow characteristics as possible, i.e. shows as little whirlas possible, the baffle plate, as seen in the direction of rotation ofthe flow of the liquid, for a portion of its length is spaced from thewall of thereservoir. Above the baffle plate, just after the inletopening in the overflow tube, a partition plate which is substantiallyvertically has been arranged which extends between the wall of thereservoir and the overflow tube and extends above the maximum liquidlevel.

Advantageously the free rim of the baffle plate is provided with adownwardly reversed part. The baffle plate thus not only causes adownwardly directed velocity component, but at the same time causes theflow to be more concentrated around the overflow tube. Hereby an areawith a more quiet flow originates above the baffle plate and between'thewall of the reservoir and the overflow tube. Moreover a final closemixing will take place because the liquid, which at last lands above thebaffle plate, at first must move downwardly and must flow around thereversed part.

Floating lumps, if any, of an added solid material are forced under theliquid level by the baffle plate, the reversed rim of the plate seeingto it that such lumps cannot land in the overflow tube. By making thereversed rim large enough not only floating, but also suspended partswill be kept in the mixing barrel, till they are completely dissolved.For this it is necessary that the reversed rim starts at the locationwhere the baffle plate comes clear from the wall of the reservoir.

- It is clear that the liquid must flow out of the nozzle with a certainforce in order to obtain the effects described above. Because of thevery close mixing in almost all cases only part of the total quantity ofthe liquid has to be worked up. The nozzle is connected with a branch ofa delivery pipe of a liquid pump and the liquid from below the overflowtube is sucked off by a liquid jet pump mounted, after the branch, inthe delivery pipe.

Because a pump does not have to bemounted in the piping through whichthe mixture is delivered from the mixing device if aggressive materialshave to be added, this has no influence on the pump. The application ofa liquid jet pump brings the advantage with it, that the liquid beingsucked from the mixing reservoir is at the same time well mixed with theliquid coming immediately from the pump. For the rest it will be-clearthat a water jet pump" can also work with other liquids.

For a good working of the mixing device it is necessary that the liquidlevel does not exceed the highest edge of the baffle plate and does notsink under the inlet opening in the overflow tube.

In order to be able to intercept the differences in pressure, whichinevitably will appear, it will be necessary to give themixing reservoira large content. For preventing this the invention now provides in theoverflow tube a level control device, which device operates a valvepresent in a bypass tube, running from a point of the delivery pipe,positioned before the water jet pump, to the mixing reservoir.

When the valve in the bypass tube is in its open position, the

liquid level, in the mixing reservoir, must with a maximum capacity ofthe water jet pump, slowly rise. When the liquid level reaches itshighest admissible point the valve in the bypass tube will closecompletely or partly. The liquid supply from the nozzle is less than theminimum suction capacity of the water jet pump.

With normal pressure differences occurring in practice a simple, and yetreliable working, devicecan be obtained by mounting in the bypass tubeas well as in the piping running towards the nozzle, a hand-operatedregulation valve, the valve in the bypass tube being completely openedor closed by the level control device.

The level control device and the valve operated by it then can be of asimple type, by which the chance of disturbances is minimal.

In order to see to it that the liquid supplied to the reservoir via thebypass tube only influences the flow in the reservoir slightly, thebypass tube can be connected with the wall of the reservoir at a pointabove the baffle plate and in such horizontal and tangential directionthat the liquid coming out of the bypass tube mainly has the same flowdirection as the main flow in the reservoir. In principle it is ofcourse also possible to connect the bypass tube with a nozzle, workingparallel with the main nozzle in the reservoir.

The invention is shown in the drawing, in which:

FIG. 1 shows a perspective view of a mixing device according to theinvention, with which the wall of the reservoir and of the overflow tubehas partly been left out;

FIG. 2 shows a vertical section over a device according to disc 3, andis provided with the longitudinal slot 5. All round the overflow tube 4the baffle plate 6 is present, which, as appears more especially fromFIG. 1, has a helical shape. The fore edge 7 of the baffle plate 6 liesabove the maximum liquid level and the back edge 8 below the minimumliquid level. At

the location of the fore edge 7 the baffle plate 6 extends itself overthe whole distance between the overflow tube 4 and the shell 2, butafter some distance the edge of the baffle plate comes clear from theshell 2 and is, from that location on, provided with a reversed rim 9,which runs on the to the back edge 8.

The back edge 8 ends at some distance beyond the longitudinal slot inthe tube 4. At the top of the plate 6 immediately after the slot 5 aplate 10 is mounted which runs between the overflow tube 4 and the wall2 of the reservoir 1 and ends above the maximum liquid level.

At the bottom of the reservoir a nozzle 11 has, in about tangentialdirection, been mounted, from which nozzle liquid is sprayed into thereservoir, such that said liquid mainly follows a flow direction asindicated with the arrow P.

Owing to the continuous liquid supply the flow will run along a helicalline with an upwardly directed pitch. The material to be added, which isadded between the edges 7 and 8 of the plate 6, Le. as seen in thedirection of flow before the edge 7, will be taken along with the liquidflow and, as far as it has not yet been mixed with the liquid then, willbe pressed against the plate 6 and obtain with the liquid a downwardvelocity so that a close mixing takes place with the liquid comingupward.

The nozzle 11 is by means of a piping 12 with a valve 13 in it,connected with the delivery pipe 14 of a pump 15, as has schematicallybeen shown in FIG. 3.

In the delivery pipe 14 a jet pump 16 is present after the branch of thepiping 12, which pump is connected with an outlet opening 17, which ispresent in the bottom 3 of the reservoir but within the periphery of theoverflow tube 4. The jet pump 16 consequently sucks the liquid treatedin reservoir 1, in the direction of the arrow Q. By the jet pump 16 theliquid treated in the reservoir 1, is mixed with the liquid that has notyet been treated, but has been supplied immediately from the pump 15.

With the embodiment shown in FIGS. 1 and 2 the delivery pipe 14 and the,jet pump 16 has been executed as a whole and has been arranged againstthe bottom 3 of the reservoir 1. Hereby a very compact construction isobtained. In most instances use can be made of synthetic materials owingto which .the construction can also be very cheap.

In order to maintain the liquid level at the desired height, between theedges 7 and 8 of the baffle plate 6, a bypass tube 18 is mounted betweenthe delivery pipe 14 and the reservoir 1. In said bypass tube 18 ahand-operated regulation stop valve 19 is present and a solenoid valve20, that is operated by means of a level-control device 21, which ispresent in the overflow tube 4, The level-control device 21 is protectedby a tube 22, mounted in the overflow tube 4 and at its upper and lowerside stands in open connection with said tube. Owing to this thelevel-control device 21 is not immediately hit by the liquid flowing viathe longitudinal slot 5 into the overflow tube 4 It is clear that thelevel-control device 21 works such, that, when the liquid leveldecreases under a certain value. the solenoid valve is opened, by whichextra liquid is supplied to the reservoir 1. Piping I8 dischargesclosely behind the plate 10 into the reservoir 1, so that the liquidcoming from the tube 18 will hardly take part in the mixing process inthe reservoir, but almost immediately will flow into the overflow tube4. Hereby a quick regulation is ensured so that the level in theoverflow tube 4 at all times is high enough to prevent air being suckedin. The tube 18 and the valves 19 and 20 must be dimensioned such, thatthe liquid level then rises slowly, so that after some time thelevel-control device 21- again will close the valve 20. The liquid levelthen decreases again and the cycle described above repeats. Instead ofan openclosed regulation of course also a proportionally working devicecan be applied, owing to which the liquid level will fluctuate verylittle, but in most instances such an arrangement, which entailsconsiderable more costs, is superfluous.

As has already been explained above there must be a certain connectionbetween the suction capacity of the pump 16, the quantities of liquidwhich land in the reservoir 1 via the tube 12 with the nozzle 11 and thebypass tube 18 and the quantity of material supplied. With the help ofthe valves 13 and 19 in tubes 12 and 18 respectively the rightquantities flowing through can be adjusted. Also with changing workingconditions, thus e.g. a varying backpressure, it appears that in mostinstances it is not necessary to change this adjustment.

It will be clear that in the above only an embodiment has been describedof the invention, and that many changes can be made without fallingoutside the inventive idea.

We claim:

1. Device, for mixing solid materials, liquids or the like in a mainliquid for obtaining a mixture, or a solution, or a suspension or thelike, said device comprising a vertically arranged substantiallycylindrical reservoir for receiving the materials to be mixed,characterized in that in the reservoir, near its bottom, at least onenozzle has been arranged connected toa supply for said main liquid andpositioned to spray said main liquid in substantially horizontal and, inview of the vertical wall of the reservoir, tangential direction, thatin the'reservoir an overflow tube has been placed the upper end of whichbeing provided with at least one inlet opening, in such a way, that theliquid in the reservoir follows an upward helical path, that at the topof the reservoir all round a part of the periphery of the overflow tubea helical-shaped baffle plate running substantially radially to the wallof the reservoir has been mounted the pitch of which, seen in thedirection of rotation of the flow of the liquid, is oppositely directedto the flow of the liquid while, seen in this direction of rotation, thefore edge of the baffle plate lies higher than the maximum liquid leveland the baffle plate at least extends till below the minimum liquidlevel and till somewhat beyond the lowest inlet point of the overflowtube.

2. Device according to claim 1, characterized in that the dischargeopening is formed by a vertical slot in the overflow tube.

3. Device according to claim 1, characterized in that the baffle plate,seen in the direction of rotation of the liquid flow, after somedistance, is lying clear from the wall of the reservoir and that abovethe plate, just after the discharge opening in the overflow tube, apartition plate running substantially vertically has been arranged whichextends itself between the wall of the reservoir and the overflow tubeand which runs on to above the maximum liquid level.

4. Device according to claim 3, characterized in that the free rim ofthe baffle plate, lying opposite to the wall of the reservoir, isprovided with a downwardly reversed part.

5. Device according to claim 1, characterized in that the nozzle isconnected with a branch of a delivery pipe of a liquid pump and that theliquid from below the overflow tube is sucked off by a water jet pumpbeing mounted, after the branch, in the delivery pipe.

6. Device according to claim 5, characterized in that in the overflowtube a level-control device has been arranged, which device operates avalve present in a bypass tube running from a point of the deliverypipe, positioned before the water jet pump, to the mixing reservoir.

bypass tube is connected with the wall of the reservoir in a pointpositioned above the baffle plate and in such a horizontal, tangentialdirection, that the liquid coming from the bypass tube mainly has thesame flow direction as has the main flow in the reservoir.

